chore: [Bigtable] configure grpc service config for PHP Bigtable

[gcf-owl-bot]

• Regenerate this pull request now.

PiperOrigin-RevId: 972068784

Source-Link: googleapis/googleapis@1182557

Source-Link: https://github.com/googleapis/googleapis-gen/commit/44cbd81232e3b93b394628be36ac3520ce6baaee
Copy-Tag: eyJwIjoiQmlndGFibGUvLk93bEJvdC55YW1sIiwiaCI6IjQ0Y2JkODEyMzJlM2I5M2IzOTQ2MjhiZTM2YWMzNTIwY2U2YmFhZWUifQ==

[JoeWang1127]

The Bigtable conformance test TestMutateRow_Generic_DeadlineExceeded failed after introducing the gRPC service configuration. With the new retry policy, MutateRow now treats DEADLINE_EXCEEDED as retryable.

During the test, a 2-second perOperationTimeout is configured against a mock server with a 10-second sleep. Previously, the test proxy only passed timeoutMillis without specifying retrySettings.totalTimeoutMillis.

When the initial 2-second call timed out with DEADLINE_EXCEEDED, GAX fell back to the default 60-second total timeout and initiated a retry. The Go mock server in cloud-bigtable-clients-test was only configured for a single request, causing a nil pointer dereference panic when the unexpected retry request arrived.

Fix this by setting retrySettings.totalTimeoutMillis in ProxyService::MutateRow, aligning it with other retryable methods (ReadRow, ReadRows, BulkMutateRows) so that GAX respects the total per-operation deadline and ceases retrying once the timeout is reached.